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Qualitative 
Chemical  Analysis 


A.  quiz  manual  and  laboratory  guide  for  the  use  of 
students  imChemistry  3a  and  3b 


University  of  Illinois 


H.  S.  Grindley,  Sc.  D. 

Professor  of  General  Chemistry 

AND 

S.  C.  Clark,  S.  B.  and  W.  A.  Redenbaugh,  Ph:  D. 
Instructors  in  General  Chemistry 


Third  Revised  Edition 
Urbana,  Illinois 
1907 


m  UBBMif 
5F  THE  . 

Kwvwarnf  IB 


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PREFACE 

This  quiz  manual  and  laboratory  guide,  which  has  ex- 
$  isted  in  one  form  or  another  for  several  years,  is  a  distinct 
}  product  of  the  growth  of  the  department  of  chemistry  in 
Oq  the  University  of  Illinois.  It  is  designed  for  use  in  the 
courses  in  qualitative  analysis  offered  in  the  first  year  in 
this  University.  These  courses  presume  the  completion 
of  Chemistry  1 ,  or  of  one  year’s  work  in  chemistry  in  a  good 
high  school.  The  quiz  manual,  which  is  intended  to  aid 
and  to  assist  the  student  in  getting  his  bearings  in  a  field 
of  activity  somewhat  new,  contains  an  outline  of  all  of  the 
work  attempted  in  Chemistry  3a  and  in  Chemistry  3b.  The 
laboratory  guide  and  notebook  on  the  other  hand,  con¬ 
tains  only  the  directions  for  those  experimental  operations, 
which  the  student  is  expected  to  perform  in  the  laboratory, 
such  questions  as  he  must  answer  at  the  time  in  the  course 
of  his  laboratory  work,  and  the  forms  for  the  experimental 
records. 

The  authors  wish  to  acknowledge  their  indebtedness  to 
many  who  have  written  on  the  subject  of  general  inorganic 
chemistry  and  qualitative  analysis  and^to  those  who  have 
taught  in  the  elementary  courses  in  chemistry  in  the  Uni¬ 
versity  of  Illinois;  acknowledgments  areTespecially  due  to 


IV 


PREFACE 


Dr.  G.  McP.  Smith,  who  has  taken  an  unusual  interest  in  this 
revision.  Dr.  P.  F.  Trowbridge,  Miss  A.  V.  Flather,  Dr.  W. 
M.  Dehn,  and  Mr.  G.  T.  Davis  have  also  given  valuable 
suggestions.  For  any  errors  of  fact,  typography,  or  expres¬ 
sion,  the  authors  alone  are  responsible.  They  will  be  glad 
to  receive  in  writing  any  and  all  suggestions  for  the  im¬ 
provement  of  the  book. 

H.  S.  G. 

S.  C.  C. 

W.  A.  R. 


PART  I 


Chemistry  3a  and  3b 

A  QUIZ  MANUAL  AND  LABORATORY  GUIDE 


CHAPTER  I 


INTRODUCTION 

SPECIAL  DIRECTIONS  TO  THE  STUDENT 

THE  METHOD  OF  PROCEDURE  IN  THE  LABORATORY  WORK 

The  first  experiment  in  the  laboratory  is  a  study  of  the 
solubility  of  the  chlorides  of  the  metals  in  water  and  in  di¬ 
lute  hydrochloric  acid.  Instead  of  using  prepared  metallic 
chlorides,  the  student  is  required  to  prepare  them  for  him¬ 
self  from  the  solutions  of  the  salts  of  the  metals8. 

Researches  in  chemistry  have  demonstrated  that,  if  a 
solution  of  sodium  chloride,  for  instance,  is  added  to  a 
solution  of  potassium  nitrate,  potassium  chloride  and  sod¬ 
ium  nitrate  are  formed  in  greater  or  less  quantity.  It  has 
also  been  proved  that,  if  a  solution  of  hydrochloric  acid  is 
added  to  a  solution  of  sodium  sulphate,  sodium  chloride 
and  sulphuric  acid  are  formed  in  greater  or  less  quantity. 
Since  these  facts  are  true,  it  is  evident  that  the  chloride  of 
any  metal  can  be  prepared  by  adding  either  hydrochloric 
acid  or  the  solution  of  any  soluble  metallic  chloride  to  a  so¬ 
lution  of  any  soluble  salt  of  this  metal.  In  this  manner  both 
the  soluble  and  the  insoluble  metallic  chlorides  are  formed. 
If  the  resulting  chloride  is  soluble  under  the  conditions  of 
the  experiment,  it  is  not  precipitated  and  the  solution  re¬ 
mains  clear.  On  the  other  hand,  if  the  resulting  chloride  is 


2  GENERAL  DIRECTIONS  FOR  LABORATORY  WORK 

insoluble  in  the  surrounding  medium,  it  is  precipitated  and 
the  solid  usually  settles  to  the  bottom  of  the  vessel  leaving 
a  clear  zone  of  liquid  above.  In  a  like  manner,  any  series  of 
salts  that  it  is  desired  to  study  can  be  prepared  by  adding 
the  proper  reagents  to  soluble  salts  of  the  metals. 

Every  experiment  in  the  laboratory  guide  should  be  per¬ 
formed  exactly  as  directed  and  the  results  should  be  record¬ 
ed  while  the  experiment  is  under  way.  After  an  experi¬ 
ment  is  finished,  the  conclusions  should  be  reported  as  indi¬ 
cated  in  the  appendix19-25.  Reference  is  made  by  means 
of  small  index  figures  to  specific  paragraphs  in  the  appendix 
in  connection  with  nearly  all  of  the  experiments.  These  ref¬ 
erences  are  notes  of  general  application  or  they  contain  in¬ 
formation  of  especial  interest  to  the  subject  in  hand. 

GENERAL  DIRECTIONS  FOR  LABORATORY  WORK 

In  the  laboratory  read  intelligently  and  work  carefully. 
Be  thoughtful,  use  your  own  reasoning  powers,  and  work  in¬ 
dependently.  It  is  essential  for  the  best  work  that  you 
isolate  yourself  from  others  in  the  laboratory,  so  that  you 
can  concentrate  your  energy  and  attention  upon  the  work 
in  hand.  Information  gleaned  from  other  students  fre¬ 
quently  is  incorrect,  often  seriously  disturbs  the  one  from 
whom  it  is  sought,  and  always  tends  to  create  more  or  less 
confusion  in  the  laboratory. 

Refer  continually  to  your  notes  on  last  semester’s  work 
and  to  the  laboratory  guide  in  Chemistry  1,  in  particular  to 
pages  5-8  and  xiii-xxxii.  Keep  in  mind  the  cautions 


THE  PRELIMINARY  RECITATION 


3 


there  given,  as  many  of  them  apply  in  a  deeper  sense  in 
qualitative  analysis. 

Reagents  must  be  kept  absolutely  free  from  contamina¬ 
tion  of  any  kind.  Do  not  interchange  the  stoppers  of  bot¬ 
tles  nor  lay  a  stopper  down  while  pouring  a  liquid  out  of  a 
bottle  but  hold  the  stopper  between  your  first  and  second, 
or  third  and  fourth,  fingers.  Keep  the  reagent  bottles  on 
your  desk  clean  and  in  the  proper  order6,7.  Never  dip  a 
pipette  nor  a  glass  rod  into  a  reagent  bottle  but  pour  out 
what  is  needed.  Never  return  any  of  a  reagent  to  a  stock 
bottle. 

As  cleanliness  and  neatness  are  absolutely  essential  to 
careful  and.  accurate  work  in  qualitative  analysis,  keep  the 
interior  and  the  exterior  of  your  desk  clean,  neat,  and  in 
order. 

Clean  all  apparatus  with  care  and  keep  it  clean.  Esti¬ 
mates  of  the  proficiency  of  your  work  will  be  made  constant¬ 
ly  both  from  the  general  appearance  of  your  desk  and  ap¬ 
paratus  and  from  the  character  of  your  work  at  the  desk. 

THE  PRELIMINARY  RECITATION 

Read  the  notices  on  the  bulletin  boards  on  the  first  floor 
of  the  chemical  building  and  consult  the  lists  of  assign¬ 
ments  to  laboratory  and  quiz  sections  posted  to  the  left  of 
the  stairway.  See  that  your  name  appears  on  the  right  lists. 
Attend  punctually  the  preliminary  recitation  for  your  lab¬ 
oratory  section,  receive  your  desk  assignment  and  ascer¬ 
tain  that  everything3  is  in  your  desk  and  in  good 
condition.  Obtain  your  class  and  laboratory  books 


4 


ARRANGEMENT  OF  THE  WORK 


and  write  your  name  in  ink  on  the  front  cover  of  each. 
Without  special  permission,  do  not  remove  your  labora¬ 
tory  guide  from  the  room  nor  bring  in  for  use  there  any  other 
text.  The  laboratory  records  are  valuable  as  an  aid  to,  not 
as  a  substitute  for,  the  memory,  and  the  manner  in  which 
they  are  kept  shows  the  character  of  the  student’s  work  as 
nothing  else  can19-25. 

HOW  TO  USE  THE  CLASS  NOTEBOOK 

The  class  study  covers  the  same  ground  as  does  the  labo¬ 
ratory  work.  The  class  notebook  is  intended  for  use  in  con¬ 
nection  with  the  class  work.  While  the  laboratory  records 
give  facts  developed  in  experimental  work,  the  class  note¬ 
book  may  include  notes  gleaned  from  any  source  and  equa¬ 
tions  other  than  those  required.  It  is  best,  however,  to 
state  the  source'of  what  is  incorporated  and  these  equations 
and  notes  must  be  kept  apart  in  the  back  part  of  the  note¬ 
book.  In  the  front  part  of  the  notebook  there  should  be 
placed  only  the  specific  equations  and  problems  called  for 
each  week  and  the  book  should  be  handed  promptly  to  your 
instructor27-30. 

ARRANGEMENT  OF  THE  WORK  IN  QUALITATIVE 
ANALYSIS 

The  work  of  the  student  in  these  courses  includes  four 
distinct  lines  of  activity;  namely,  the  recitations,  the 
written  quizzes  and  final  examination,  the  preliminary 
laboratory  exercises  and  laboratory  manipulations  and 
methods,  and  the  “unknowns.” 


ARRANGEMENT  OF  THE  WORK 


5 


The  recitations,  or  class  exercises,  consist  of  two  oral 
quizzes  per  week  upon  assigned  portions  of  this  text,  upon 
certain  pages  in  Smith’s  General  Inorganic  Chemistry,  upon 
the  preceding  laboratory  experiments,  upon  certain  prob¬ 
lems  and  equations  involving  the  qualitative  and  quantita¬ 
tive  study  of  chemical  reactions,  and  upon  definite  refer¬ 
ences  to  a  selected  list31  of  books  in  which  the  various  topics 
in  chemistry  are  treated  fully  and  exhaustively.  The  re¬ 
sults  of  the  laboratory  work  are  discussed  in  their  proper 
connection  with  the  other  phases  of  the  class  work.  The 
class  work  in  combination  with  the  laboratory  work  aims  to 
present  a  harmonious  and  unified  development  of  the  sub¬ 
ject  of  qualitative  analysis  for  beginners. 

The  written  quiz  and  examination  work  is  grouped  as 
follows ; 

i.  Written  quizzes  given  approximately  once  in  three 
weeks  to  review  the  class  and  the  laboratory  work. 

ii.  Laboratory  quizzes  given  from  time  to  time  to  test 
the  student’s  knowledge  and  grasp  of  the  work  being  done 
by  him  in  the  laboratory. 

iii.  The  final  examination  given  for  3a  at  the  end  of 
the  semester  and  for  3b  at  the  end  of  nine  weeks. 

The  laboratory  work  requires  ten  hours  per  week  in  the 
experimental  study  of  the  principles  involved  and  the  meth¬ 
ods  employed  in  qualitative  analysis. 

As  soon  as  the  preliminary  study  of  solubility  is'  com¬ 
pleted,  the  student  takes  up  the  study  of  a  graduated  series 
of  unknowns.  These  unknowns  consist  of  a  series  of  solu- 


6 


THE  STUDENT  S  STANDING 


tions  and  solids  arranged  with  the  idea  of  developing  both 
the  method  of  analysis  and  the  student’s  powers  of  applying 
this  method  to  substances  of  greater  and  greater  complex¬ 
ity. 

THE  OFFICE  HOURS  OF  INSTRUCTORS 

Each  instructor  keeps  certain  office  hours  as  per  the  lists 
posted  on  the  bulletin  boards  and  on  each  Office  door.  The 
purpose  of  these  office  hours  is  to  give  the  students  in  Chem¬ 
istry  3a  and  3b  an  opportunity  to  meet  their  instructors 
individually  and  to  obtain  any  necessary  additional  help. 
During  their  office  hours  the  instructors  will  be  glad  to  make 
the  acquaintance  of  their  students  and  students  are  urged  to 
make  full  use  of  this  arrangement  when  really  in  need  of 
assistance.  In  the  laboratory  work  also,  the  students 
should  feel  free  to  seek  the  instructors  for  advice  and 
counsel  at  any  time.  This  does  not  mean,  however,  that  the 
instructor  should  be  consulted  by  the  student  before  the  lat¬ 
ter  has  made  full  use  of  his  own  ingenuity  and  mental  power. 

THE  STUDENT’S  STANDING 

It  should  be  clearly  understood  at  the  beginning,  that, 
in  order  to  obtain  credit  in  either  of  these  courses,  it  is 
necessary  for  the  student  to  make  a  grade  of  70  per  cent  or 
more  in  each  of  the  four  lines  of  work  above  mentioned.  If 
this  is  done  the  student’s  final  standing  is  represented  by  his 
average  grade  in  these  four  divisions  of  the  work.  A  failure 
in  any  one  of  these  divisions  of  work  precludes  credit  being 
given  for  the  course  until  the  deficiency  is  made  up.  Each 
of  the  four  lines  of  work  is  graded  separately  and  inde- 


definition  of  qualitative  analysis 


7 


pendently  and  generally  by  different  instructors.  The 
results  of  each  month’s  work  may  be  obtained  at  stated 
times  from  the  general  office,  Room  102,  as  announced  upon 
the  bulletin  boards. 

Definition  and  Aim  of  Qualitative  Analysis 

The  science  of  chemistry  deals  with  the  composition  of 
the  substances  included  in  the  material  universe,  with  the 
transformation  of  these  substances  into  each  other,  and  with 
the  phenomena  accompanying  such  changes.  Organic 
chemistry  is  a  study  of  certain  compounds  of  hydrogen  and 
carbon,  called  hydrocarbons,  and  of  their  derivatives.  In¬ 
organic  chemistry  includes  the  study  of  all  other  substances. 
Chemistry  1  dealt  mainly  with  the  non-metallic  elements. 
Chemistry  3a  and  3b  deal  mainly  with  the  characteristic  re¬ 
actions  of  a  few  of  the  commonly  occurring  metallic  ele¬ 
ments.  The  study  of  these  reactions  in  the  laboratory 
may  be  synthetical  or  analytical.  Synthesis  is  a  putting  to¬ 
gether,  a  building  up,  of  a  more  complex  substance  from 
simpler  ones.  Analysis  is  the  reverse  of  this  process.  It  is 
the  separation  of  a  compound  into  its  constituents,  or  origi¬ 
nal  components,  with  a  view  of  discovering  what  elements 
enter  into  the  combination.  If  the  amount  by  weight  or  by 
volume  of  one  or  more  of  the  constituent  elements  is  deter¬ 
mined,  the  analysis  is  quantitative.  If  only  the  elements 
present  are  determined  and  not  their  relative  quantity,  the 
analysis  is  qualitative. 

Qualitative  analysis  is  that  branch  of  chemistry  which 
treats  of  the  recognition  of  the  elements  and  of  their  com- 


8 


THE  CONTENT  OF  QUALITATIVE  ANALYSTS 


pounds.  One  of  the  first  objects  of  chemistry  is  to  ascer¬ 
tain  the  composition  of  the  substances  which  exist  so  abund¬ 
antly  and  in  such  varied  conditions  in  nature.  The  study  of 
qualitative  analysis  includes  an  investigation  and  a  compar¬ 
ison  of  the  behavior  of  the  several  elements  and  of  their  com¬ 
pounds,  a  study  of  the  phenomena  exhibited  by  them  under 
various  conditions,  and  the  determination  of  the  particular 
conditions  essential  to  the  manifestation  of  each. 

THE  BASIS  OF  QUALITATIVE  ANALYSIS 

Since  the  most  important  class  of  compounds  which  the 
metals  form  are  salts,  the  best  method  of  becoming  familiar 
with  the  metallic  elements  consists  in  the  study  of  the  prop¬ 
erties  and  of  the  reactions  of  the  salts  which  they  form. 
One  of  the  most  important  properties  of  salts  is  their  solubil¬ 
ity  in  water.  Further,  qualitative  analysis  is  based  pri¬ 
marily  upon  the  solubility  and  the  insolubility  of  certain 
metallic  salts  in  water  and  in  a  few  other  common  solvents. 
We  must  not  forget  that  the  terms  soluble  and  insoluble  are 
more  or  less  relative,  no  substance  being  absolutely  in¬ 
soluble.  Barium  sulphate  is  one  of  the  most  insoluble  com¬ 
pounds,  since  one  part  dissolves  in  344,000  parts  of  water. 
Strontium  sulphate  is  also  said  to  be  insoluble,  but  one  part 
of  this  compound  dissolves  in  6,900  parts  of  water.  One 
part  of  calcium  sulphate  dissolves  in  467  parts  of  water.  It 
also  is  commonly  said  to  be  insoluble  in  water. 

THE  CONTENT  OF  3a  AND  3b 

Fully  ninety-five  per  cent  of  the  reactions,  involved  in 
the  complete  analysis  of  substances,  take  place  in  solution. 


PRELIMINARY  CLASS  WORK 


9 


For  this  reason  the  laboratory  work  in  these  courses  begins 
with  a  study  of  the  solubilities  of  four  series  of  compounds 
which  the  twenty-six  commonly  occurring  metals  form  with 
certain  non-metallic  or  acidic  elements.  The  data  here  ac¬ 
quired  furnish  the  basis  for  the  division  of  the  metals  into 
six  analytical-groups ;  the  study  of  these  groups,  followed  by 
that  of  the  acids,  develops  into  the  analysis  of  simple  un¬ 
knowns,  and  this  in  turn  prepares  for  the  analysis  of  mix¬ 
tures  of  moderate  complexity  and  of  double  salts.  Further, 
the  student  in  3a  attempts  in  addition  the  analysis  of  mix¬ 
tures  of  greater  and  greater  complexity,  of  metals  and  al¬ 
loys,  of  selected  commercial  and  natural  products,  of  a  few 
of  the  less  commonly  occurring  substances,  and  of  com¬ 
binations  whose  ingredients  mutually  interfere  with  the 
analysis  of  each  other. 

PRELIMINARY  CLASS  WORK 

THE  ELEMENTS 

For  convenience  the  elements  are  divided  into  metals 
and  non-metals,  though  a  sharp  line  separating  the  two  can 
not  be  drawn.  The  metals  can  generally  be  readily  dis¬ 
tinguished  from  the  non-metals  by  their  physical  and  by 
their  chemical  properties,  i.  The  non-metals  usually  lack 
the  characteristic  luster,  which  the  metals  possess,  and  the 
non-metals  are  poor  conductors  of  heat  and  of  electricity, 
while  the  metals  are  good  conductors,  ii.  The  non-met¬ 
als  unite  with  oxygen  to  give  acidic  anhydrides,  that  is, 
compounds  which  are  capable  of  combining  with  water  to 
form  acids.  The  metals,  combined  with  oxygen,  form  bas- 


10 


PHYSICAL  PROPERTIES  OF  THE  METALS 


ic  anhydrides,  that  is,  compounds  which  with  the  elements 
of  water  give  bases  or  hydroxides.  Hydroxides  are  capa¬ 
ble  of  neutralizing  acids.  The  metals  are  capable  of  replac¬ 
ing  the  hydrogen  of  acids.  In  both  cases  salts  are  formed. 

THE  METALS 

OCCURRENCE  AND  EXTRACTION  FROM  ORES 

According  to  the  periodic  classification34  of  the  elements 
most  of  the  commonly  occurring  metallic  elements  are  in 
Families  I,  II,  III,  and  VIII.  The  exceptions  are  as  fol¬ 
lows:  Tin  and  lead  occur  in  Family  IV ;  arsenic,  antimony, 
and  bismuth,  in  Family  V;  chromium,  in  Family  VI;  and 
manganese,  in  Family  VII. 

The  metals  occur  in  nature  in  many  different  minerals 
and  ores.  They  usually  occur  most  abundantly  either  as 
oxides,  sulphides,  carbonates,  or  sulphates.  The  most  com¬ 
mon  method  of  extracting  the  metals  from  their  naturally 
occurring  compounds  is  that  used  in  the  case  of  iron,  which 
consists  in  heating  its  oxides  with  charcoal.  If  the  ores  are 
not  oxides  they  are  converted  into  the  oxides  by  heating 
them  in  contact  with  the  air.  By  this  treatment  the  nat¬ 
ural  carbonates,  hydroxides,  and  sulphides  are  changed  into 
the  oxides,  which  may  then  be  reduced  by  heating  with 
carbon. 

PHYSICAL  PROPERTIES  OF  THE  METALS 

At  ordinary  temperatures  all  of  the  metals  excepting 
mercury  are  solid,  opaque  bodies.  In  compact  masses  they 
exhibit  metallic  luster  and  most  of  them  possess  a  light  grey 


CHEMICAL  PROPERTIES  OF  THE  METALS 


11 


color;  gold  and  copper  are,  however,  brilliantly  colored.  In 
the  form  of  a  powder  almost  all  of  the  metals  are  black. 

The  metals  are  good  conductors  of  heat  and  of  electric¬ 
ity.  The  specific  gravity  of  the  metals  varies  widely,  from 
0.59  in  the  case  of  lithium  to  22.5  in  the  case  of  osmium.  In 
general  the  specific  gravities  of  the  metals  increase  with  the 
atomic  weights.  Metals,  whose  specific  gravities  are  below 
5,  are  called  light  metals;  and  those,  whose  specific  gravities 
are  above  5,  are  called  heavy  metals.  Most  metals  are 
malleable  and  tough  and  may  be  converted  into  foil  and 
wire.  Gold  and  silver  are  the  most  malleable  of  the  metals. 
Arsenic,  antimony,  bismuth,  and  tin,  which  possess  the 
characteristics  both  of  metals  and  of  non-metals,  are  brittle. 

CHEMICAL  PROPERTIES  OF  THE  METALS 

As  a  rule  metals  do  not  combine  with  hydrogen  but  direct¬ 
ly  or  indirectly  they  all  form  compounds  with  oxygen.  Their 
oxygen  compounds  generally  have  the  character  of  basic  an¬ 
hydrides;  that  is,  they  form  bases  or  hydroxides  with  the 
elements  of  water.  This  is  markedly  true  only  of  the  alkali 
and  alkaline-earth  metals.  Under  ordinary  conditions,  most 
metals  are  not  soluble  in  water,  except  in  the  cases  where 
they  react  chemically  with  water,  for  example  the  metals  of 
Groups  I  and  II,  according  to  MendeleefFs  classification  of 
the  elements,  react  with  water  forming  more  or  less  soluble 
hydroxides  of  the  metals  and  liberating  hydrogen.  Many 
metals  react  directly  with  acidb  forming  salts. 


12 


REVIEW  QUESTIONS 


Questions 

Reference  in  Smith:  Pages  530-539 

From  time  to  time,  a  number  of  questions  upon  the 
class  work  and  upon  the  laboratory  experiments  will  be  in¬ 
cluded.  These  questions  may  also  cover  the  work  of  last 
semester  in  Chemistry  1.  All  of  these  questions  can  be 
answered  from  the  preceding  pages  of  this  manual,  from 
Smith’s  General  Inorganic  Chemistry,  from  your  notes  upon 
the  class  work,  from  the  preceding  laboratory  experiments, 
or  from  the  reference  books.  These  questions  are  the  basis 
for  the  oral  quizzes  and  for  the  written  quizzes  and  final  ex¬ 
amination. 

What  happens  when  a  solution  of  sodium  chloride  is  add¬ 
ed  to  one  of  potassium  nitrate?  When  a  solution  of  hydro¬ 
gen  chloride  is  added  to  one  of  sodium  sulphate?  How  may 
we  prepare  any  series  of  salts  of  the  metals?  What  evi¬ 
dence  have  we  that  any  member  of  such  a  series  is  insoluble? 
With  what  does  the  science  of  chemistry  deal?  inorganic 
chemistry?  Distinguish  between  synthesis  and  analysis'. 
Between  quantitative  and  qualitative  analysis?  Define 
qualitative  analysis.  Upon  what  is  qualitative  analysis 
primarily  based.  Show  that  the  terms  soluble  and  insolu¬ 
ble  are  relative.  Into  what  two  classes  may  elements  be 
divided?  Give  the  characteristic  physical  and  chemical 
properties  of  each  class.  Where  do  the  metals  appear  in  the 
periodic  table?  How  do  they  occur  in  nature?  How  are 
they  extracted  from  their  ores?  Mention  the  chief  phys¬ 
ical  properties  of  metals.  The  chief  chemical  properties. 


NOMENCLATURE 


13 


Why  are  the  physical  properties  of  metals  of  great  im¬ 
portance  to  the  chemist  ?  Show  what  is  meant  by  each  of  the 
following  terms;  metallic  luster,  crystallized  form,  specific 
gravity,  malleable,  tenacity,  melting  point,  boiling  point, 
alloy,  amalgam,  conductivity.  Illustrate  each  term  by  ex¬ 
amples.  What  are  the  chief  chemical  properties  of  the  met¬ 
als?  Show  how  the  hydrolysis  of  the  halogen  compounds 
can  be  used  to  distinguish  metals  from  non-metals?  What 
is  a  complex  acid?  Write  the  formulas  for  several  salts  of 
complex  acids.  How  do  these  salts  behave  in  a  reaction? 
How  may  the  metallic  elements  be  grouped  according  to  the 
periodic  system,  that  is,  according  to  their  chemical  rela¬ 
tions?  Name  the  principal  representatives  of  each  of  the 
eleven  families.  Give  their  characteristic  chemical  prop¬ 
erties. 

SOME  GENERAL  PRINCIPLES  OF  THE  NOMEN¬ 
CLATURE  OF  INORGANIC  COMPOUNDS 

A.  ACIDS 

An  acid  consists  of  a  non-metal,  or  of  a  group  of  non- 
metals,  joined  to  hydrogen,  which  is  replaceable  by  a  metal. 

1.  Hydracids 

These  are  binary  acids  which  contain  but  one  negative 
element  or  group  of  elements,  and  hydrogen.  They  are 
named  by  prefixing  “hydro-”  to  the  name  of  the  negative 
elements,  giving  it  the  ending  “-ic”,  and  adding  the  term 
acid  (see  also  C,  1,  a,  i.) 


14 


NOMENCLATURE 


H2F2,  hydrofluoric  acid  H2S,  hydrosulphuric  acid 

HC1,  hydrochloric  acid  H2Te,  hydrotelluric  acid 

HBr,  hydrobromic  acid  HCN,  hydrocyanic  acid 

HI,  hydriodic  acid  H4Fe(CN)6,  hydroferrocyanic 

acid 

2.  Acids  Other  Than  Hydracids 

These  acids  contain  oxygen,  or  sulphur  in  addition  to  an¬ 
other  negative  element.  They  are  named  from  their  char¬ 
acteristic  negative  element. 

a.  If  only  one  acid,  containing  a  given  characteristic 
negative  element,  exists,  it  is  named  by  changing  the  ending 
of  this  element  to  “-ic”  and  adding  the  term  acid. 

H2C03,  carbonic  acid  H2Mo04,  molybdic  acid 

b.  If  several  acids,  containing  the  same  characteristic 
negative  element,  exist,  they  are  named  as  follows: 

i.  The  oldest,  the  best  known,  or  the  most  stable  acid  is 
given  the  ending  “-ic”.  The  acid,  containing  proportion¬ 
ally  less  oxygen  than  the  “-ic”  acid,  is  given  the  ending 
‘  ‘  -ous  ” . 

HN03,  nitric  acid  H2S04,  sulphuric  acid 

HN02,  nitrous  acid  H2S03,  sulphurous  acid 

ii.  The  acid,  containing  proportionally  more  oxygen 
than  the  “-ic”  acid,  has  the  prefix  “per-”  added  to  the 
name  of  the  “-ic”  acid;  while  the  acid,  containing  less  oxy¬ 
gen  proportionally  than  the  “-ous”  acid,  has  the  prefix 
“hypo”  added  to  the  name  of  the  “ous”  acid. 


NOMENCLATURE 


15 


HCIO,  hypochlorous  acid  H2S204,  hyposulphurous  acid 
HC102,  chlorous  acid  H2S03,  sulphurous  acid 
HC103,  chloric  acid  H2S04,  sulphuric  acid 

HC104,  perchloric  acid  H2S208,  persulphuric  acid 

c.  The  same  acid  anhydride  may  unite  with  varying 
amounts  of  water  to  form  acids  in  which  the  characteristic 
negative  element  is  in  the  same  state  of  oxidation.  In  such 
cases  the  preceding  rules  alone  can  not  be  applied.  Such 
acids  are  distinguished  from  each  other  by  the  prefixes 
‘‘ortho-”,  “pyro-”  or  “di-”,  and  “meta-”. 

P205  +  3H20  =  2H3P04,  orthophosphoric  acid 
P205  +  2H20  =  H4P207,  pyrophosphoric  acid 
P205  +  H20  =  2HP03,  metaphosphoric  acid 

d.  There  are  several  acids,  analogous  to  some  of  the 
above  oxygen  acids,  but  with  .one  or  more  sulphur35  atoms 
substituted  for  the  oxygen.  They  are  named  as  in  a,b,  and 
c, but  with  “thio-”,  “sulpho-”,  or  “sulph-”  prefixed  to  the 
name  of  the  characteristic  negative  element. 

H2Sn03,  stannic  acid  H2S04,  sulphuric  acid 
H2SnS3  sulphostannic  acid  H2S203,  thiosulphuric  acid 

e.  Acids  are  said  to  be  monobasic,  dibasic,  tribasic,  tet- 
rabasic,  etc.,  accordingly  as  they  contain  one,  two,  three, 
four,  or  more  replaceable  hydrogen  atoms.  HC1,  H2S04, 
H3P04,  etc. 

B.  BASES  OR  HYDROXIDES 

Bases  have  the  hydroxyl  group,  OH,  united  to  a  metal, 
a.  In  naming  bases,  the  name  of  the  metal  is  first  men¬ 
tioned  followed  by  the  term  hydroxide36. 


16 


NOMENCLATURE 


NaOH,  sodium  hydroxide 
NH4OH,  ammonium  dydroxide 
Sr(OH)2,  strontium  hydroxide 
Al(OH)3,  aluminum  hydroxide 

b.  In  case  there  are  two  hydroxides  of  the  same  metal, 
the  ending  of  the  name  of  the  metal  is  changed  to  “-ic-”  or 
“-ous”  depending  upon  whether  there  is  proportionally  a 
greater  or  a  less  number  of  hydroxyl  groups  in  the  com¬ 
pound. 

Co(OH)3,.  cobaltic  hydroxide 
Co(OH)2,  cobaltous  hydroxide 
Sn(OH)4,  stannic  hydroxide 
Sn(OH)2,  stannous  hydroxide 
Fe(OH)3,  ferric  hydroxide 
Fe(OH)2,  ferrous  hydroxide 

c.  Bases  are  said  to  be  monacid  bases,  diacid  bases,  etc. 
accordingly  as  they  contain  one,  two,  or  more  hydroxyl 
groups. 

NaOH,  Ca(OH)2  Al(OH)s,  Sn(OH)4. 

C.  COMPOUNDS  OTHER  THAN  ACIDS  AND  BASES 
1.  Compounds  of  Two  Elements 
This  class  consists  of  all  binary  compounds  including 
hydracids  and  their  salts  but  the  hydracids  are  usually 
named  in  accordance  with  A,  1. 

a,  i.  They  are  named  by  mentioning  the  more  posi¬ 
tive  (metallic)  element  first,  followed  by  the  name  of  the 
more  negative  (non-metallic)  element  with  its  ending 
changed  to  “-ide”. 


NOMENCLATURE 


17 


Na2S,  sodium  sulphide 
CaC2,  calcium  carbide 
BaF2,  barium  fluoride 
HC1,  hydrogen  chloride 


KC1,  potassium  chloride 
BN,  boron  nitride 
MgO,  magnesium  oxide 
H2S,  hydrogen  sulphide 


ii.  Sometimes  a  group  of  elements  react  as  a  single  ele¬ 
ment,  for  example: 

(NH)4Br,  ammonium  bromide 
K(CN),  potassium  cyanide 

b.  There  may  be  more  than  one  compound  of  the  same 
two  elements.  The  rule  in  a  is  used  with  one  of  the  follow¬ 
ing  modifications : 

i.  The  ending  of  the  name  of  the  more  positive  element 
is  changed  to  ‘  ‘-ic  ”  or  ‘  ‘-ous  ”  depending  upon  whether  the 
proportional  amount  of  the  more  negative  element  is  greater 
or  less. 

FeCl3,  ferric  chloride  Cu202  (CuO),  cupric  oxide 
FeCl2,  ferrous  chloride  Cu20,  cuprous  oxide 

ii.  The  prefixes  “mono-”,  “di-”,  “tri-”,  “tetra-”, 

“penta-”,  etc.,  are  applied  depending  upon  whether  there 
are  one,  two,  three,  four,  five,  or  more  atoms  of  the  more 
negative  element. 

N20,  nitrogen  monoxide 

N202(N0),  nitrogen  dioxide 
N203,  nitrogen  trioxide 

N204(N02),  nitrogen  tetroxide 
N205,  nitrogen  pentoxide 

SbCl3,  antimony  trichloride 

SbCl5,  antimony  pentachloride 

SbH3,  antimony  trihydride 


18 


NOMENCLATURE 


H202,  hydrogen  dioxide 

Mn207,  manganese  heptoxide 

2.  Salts  of  Acids  Other  Than  Hydracids 
Salts  may  be  conceived  of  as  derived  from  acids  by  the 
replacement  of  the  hydrogen  of  the  acid  by  a  metal. 

a,  i.  The  salt  is  usually  named  by  mentioning  the 
metal  first,  followed  by  the  name  of  the  acid  with  the  ending 
“-ic”  changed  to.  “-ate”  or  the  ending  “-ous”,  to  “-ite”. 

HCIO,  hypochlorous  acid 
KCIO,  potassium  hypochlorite 

HC102,  chlorous  acid 
KC102,  potassium  chlorite 

HC103,  chloric  acid 
KCIO3,  potassium  chlorate 

HC104,  perchloric  acid 
KC104,  potassium  perchlorate 

H2Sn02,  stannous  acid 
Na2Sn02,  sodium  stannite 

H2SnS2,  sulphostannous  acid 
Na2SnS2,  sodium  sulphostannite 

HP03,  metaphosphoric  acid  # 

NaP03,  sodium  metaphosphate 
H2C204,  oxalic  acid 
(NH4)2C204,  ammonium  oxalate 

ii.  The  salts  of  hydracids  are  not  named  according  to 
this  rule  for  the  reason  that  such  salts  consist  of  but  two 


NOMENCLATURE 


19 


elements  and  hence  take  the  ending  “-ide”  as  in  C,  1,  a,  i. 

HC1,  hydrochloric  acid 

NaCl,  sodium  hydrochlorate  or,  usually,  sodium  chloride. 

iii.  If  the  valence  of  the  metal  makes  it  possible  for 
two  salts  of  the  same  acid  to  be  formed,  the  ending  “-ic”  or 
“-ous”  is  applied  to  the  name  of  the  metal  depending  upon 
whether  the  proportional  amount  of  the  negative  element  is 
greater  or  less. 

Fe2(S04)3,  ferric  sulphate  FeS04,  ferrous  sulphate 

b.  When  all  of  the  hydrogen  of  an  acid  is  replaced  by  a 
metal,  the  salt  is  called  a  normal  or  neutral  salt  and  then  the 
nomenclature  in  a,  above,  is  used.  If  only  a  part  of  the  hy¬ 
drogen  is  replaced  by  the  metal,  the  salt  is  called  an  acid  salt 
and  the  following  modifications  in  nomenclature  are  intro¬ 
duced 

i.  In  the,  case  of  acid  salts  of  dibasic  acids,  the  term 
acid  is  placed  before  the  name  of  the  salt. 

NaHS04,  acid  sodium  sulphate 

KHC03,  acid  potassium  carbonate 

Sodium  bisulphate  and  potassium  bicarbonate,  respec¬ 
tively,  are  frequently  used  also.  Neutral  or  normal  sodium 
sulphate  or  potassium  carbonate  are  sometimes  used  in 
order  to  accentuate  the  difference  between  the  two 
sodium  salts  of  sulphuric  acid  or  the  two  potassium  salts  of 
carbonic  acid. 

ii.  In  the  case  of  salts  of  tribasic  acids,  the  term  pri¬ 
mary  or  monobasic,  secondary  or  dibasic,  tertiary  or  tribasic, 
is  placed  before  the  name  of  the  salt  depending  upon  wheth- 


20 


NOMENCLATURE 


er  one,  two,  or  three  of  the  hydrogen  atoms  of  the  acid  have 
been  replaced  by  a  metal. 

NaH2P04,  primary  sodium  phosphate,  monobasic  sod¬ 
ium  phosphate,  or  monosodium  phosphate. 

Na2HP04,  secondary  sodium  phosphate,  dibasic  sod¬ 
ium  phosphate,  or  disodium  phosphate. 

Na3P04,  tertiary  sodium  phosphate,  tribasic  sodium 
phosphate,  or  trisodium  phosphate. 

iii.  In  the  case  of  salts  of  acids,  containing  more  than 
three  replaceable  hydrogen  atoms,  the  method  outlined  in  i 
or  ii  is  usually  adapted. 

K4Sb207,  potassium  pyroantimonate 

H2K2Sb207,  acid  potassium  pyroantimonate 

c.  When  all  of  the  hydroxyl  groups  of  the  base  are  not 
replaced  by  acid  groups,  the  salt  is  called  a  basic  salt.  The 
following  examples  indicate  the  nomenclature. 

Cu2(0H)2C03,  basic  cupric  carbonate 

BiOCl,  basic  bismuth  chloride  or  bismuth  oxychloride 

BiON03,  basic  bismuth  nitrate,  bismuth  oxynitrate,  or 
bismuth  subnitrate 

KSb0C4H406,  potassium  antimonyl  tartrate  or  tartar- 
emetic 

CaClOCl,  ‘  ‘chloride  of  lime”  or  bleaching  powder 

d.  When  the  hydrogen  atoms  are  replaced  partly  by 
one  metal  and  partly  by  others,  the  salt  is  called  a  mixed  salt 
and  is  named  accordingly. 

CoNi(S04)2,  cobalt  nickel  sulphate 

MgNH4P04,  magnesium  ammonium  phosphate 


CLASSIFICATION  OF  SALTS 


21 


FORMATION  OF  SALTS 

Salts  are  compounds  of  the  metals  with  acid  radicals. 
They  are  formed  in  many  cases  by  the  reaction  of  a  metal 
with  an  acid.  Salts  are  also  formed  by  the  reaction  of  a 
base,  or  of  a  basic  anhydride,  with  an  acid,  In  place  of  the 
acid,  its  anhydride  may  be  substituted22. 

Zn  +  2HC1  =  ZnCl2  +  Ha 
Fe  +  H2S04  =  FeS04  +  H2 
NaOH  +  HC1  =  NaCl  +  H20 
Na2Q  +  H2S04  =  Na2S04  +  H20 
Ba(OH)2  +  H2S04  =  BaSQ4  +  2H20 
CuO  +  2HN03  =  Cu(N03)2  +  H20 
2KOH  +  C02  -  K2C03  +  H20 
CaO  +  SO,  =  CaS04 

3Cu  +  8HN03  =  3Cu(N03)2  +  2NO  +  4H20 

CLASSIFICATION  OF  SALTS 

Salts  may  be  arranged  with  reference  to  the  periodic 
classification  of  their  characteristic  negative  elements. 

a,  i.  Fluorides,  chlorides,  bromides,  and  iodides  con¬ 
sist  of  metals  in  combination  with  fluorine,  chlorine,  brom¬ 
ine,  and  iodine. 

ii.  Chlorates  and  permanganates  are  salts  of  the  chief 
oxyacids  of  chlorine  and  manganese,  respectively. 

b,  i.  Sulphides  consist  of  metals  combined  with  sul¬ 
phur. 

ii.  Sulphates,  sulphites,  and  thiosulphates  are  salts  of 
the  chief  oxyacids  of  sulphur. 


22 


REVIEW  QUESTIONS 


iii.  Chromates  and  dichromates  are  salts  of  the  corres¬ 
ponding  oxyacids  of  chromium. 

c,  i.  Nitrates  and  nitrites  consist  of  the  acids  of  nitro¬ 
gen  (nitric  and  nitrous)  in  which  the  hydrogen  has  been  re¬ 
placed  by  metals. 

ii.  Phosphates,  arsenates  and  arsenites,  and  antimo- 
nates  and  antimonites,  are  salts  of  the  oxyacids  of  phosphor¬ 
us,  arsenic,  and  antimony. 

d,  i.  Carbonates  are  salts  of  carbonic  acid.  Salts  of 
other  acids,  containing  carbon,  are  also  included;  as  ace¬ 
tates,  oxalates,  and  tartrates. 

ii.  Silicates  are  derived  from  salts  of  the  various  silicic 
acids. 

e,  Borates  are  derived  from  boric  acid. 

Questions 

Reference  in  Smith:  Pages  539  to  545  and  263  to  265 

Students  in  this  course  should  understand  thoroughly 
the  meaning,  and  be  able  to  define  and  to  illustrate  completely 
the  following  terms  which  were  met  with  in  the  work  of  the 
the  last  semester: — Acid,  base,  salt,  metal,  non-metal,  chem¬ 
ical  symbol,  chemical  formula;  valence,  univalent,  bivalent, 
trivalent,  quadrivalent;  basicity  of  acids,  monobasic  acids, 
dibasic  acids,  tribasic  acids,  acidity  of  bases,  monacid  bases, 
diacid  bases,  triacid  bases,  normal  salt,  acid  salt,  basic  salt, 
primary,  secondary,  and  tertiary  salts. 

Of  what  does  an  acid  consist?  Define  hydracids.  Give 
four  examples.  Define  oxyacids.  Give  several  examples. 
How  are  hydracids  usually  named?  How  are  oxyacids 


REVIEW  QUESTIONS 


23 


named?  How  are  two  oxyacids  containing  the  same  char¬ 
acteristic  negative  element  distinguished  from  each  other? 
How  are  several  such  acids  distinguished  from  each  other? 
How  are  several  oxyacids,  containing  the  same  character¬ 
istic  negative  element  in  the  same  state  of  oxidation,  dis¬ 
tinguished  from  each  other?  What  is  the  relation  of  sul¬ 
phur  to  oxygen  in  some  acids?  Give  examples  of  each  of 
these  classes  of  acids. 

Of  what  does  a  base  consist?  How  are  they  named? 
How  are  two  hydroxides  of  the  same  metal  distinguished 
from  each  other?  What  other  classes  of  compounds  are 
there?  What  is  a  binary  compound?  How  are  they 
named?  How  are  two  compounds'  of  the  same  two  ele¬ 
ments  usually  distinguished  from  each  other?  Give  another 
general  method  for  distinguishing  more  than  one  com¬ 
pound  of  the  same  two  elements.  Give  examples  of  each  of 
these  classes  of  compounds. 

What  is  a  salt?  How  are  salts  of  oxyacids  usually 
named?  Of  hydracids.  Give  several  examples  of  each. 
What  is  the  effect  of  the  valence  of  the  metal  upon  the 
name  of  the  salt?  Define  neutral  salt.  Acid  salt.  How 
are  acid  salts  of  dibasic  acids  named?  Of  tribasic  acids? 
What  is  a  basic  salt?  How  are  basic  salts  usually  named? 
What  is  a  mixed  salt?  How  are  they  named?  Give  ex¬ 
amples  of  all  these  classes  of  substances.  Name  three  ways 
in  which  a  salt  may  be  formed.  Give  equations  to  illustrate 
each  method  of  preparation.  How  may  salts  be  classified 
according  to  the  periodic  system? 


24 


REVIEW  QUESTIONS 


How  do  the  metals  usually  occur  in  nature?  Discuss 
the  metallurgy  of  ores  in  which  the  metals  occur  native.  In 
which  the  ore  is  an  oxide.  A  carbonate.  A  sulphide.  A 
chloride  or  a  fluoride.  What  use  is  made  of  electrolysis 
in  extracting  metals  from  their  ores? 

What  is  an  acid  ?  What  is  the  replaceable  part  of  an  acid  ? 
What  is  meant  by  the  basicity  of  an  acid?  Illustrate  the 
meaning.  Define  monobasic  acids,  dibasic  acids,  tribasic 
acids,  and  give  examples  of  each.  What  is  the  basicity  of 
the  following  acids: —  HC1,  HBr,  HI,  H2S,  HC2H302, 
H3P04,  H2S04,  H3As04,  H4Si04,  H2S03,  HC103,  H2C4H406? 

What  is  the  meaning  of  the  term  acidity  of  bases  ?  Give 
examples  which  illustrate.  Define  monacid  bases,  diacid 
bases,  triacid  bases,  and  give  examples  of  each.  What 
is  the  acidity  of  the  following  bases: —  KOH, 
Al(OH)s,  Ca(OH)2,  Fe(OH)s,  Zn(OH)2,  NaOH,  Fe(OH)2. 

What  is  a  normal  salt  ?  A  secondary  salt  ?  A  primary 
salt?  A  tertiary  salt?  An  acid  salt?  A  basic  salt? 
Explain  the  uses  of  the  prefixes  mono,  di,  tri,  etc.,  in  naming 
salts.  Give  examples  of  all  of  the  above  classes  of  salts. 

Explain  the  use  of  the  suffixes  “ic”  and  “ous”  in 
naming  acids,  bases,  and  salts.  Explain  the  use  of  the 
termination  “ate”  and  ’‘ite”  in  naming  salts.  Also  ex¬ 
plain  the  use  of  the. prefixes  “hypo”  and  “per”  in  naming 
salts  and  acids.  Give  examples  which  illustrate  the  use  of 
all  of  these  terms. 

What  are  oxides  of  metals?  Give  several  methods  of 


REVIEW  QUESTIONS 


25 


preparation.  What  are  their  general  physical  and  chemi¬ 
cal  properties  ?  What  are  hydroxides  of  metals  ?  Give  two 
methods  of  preparation.  Give  their  chief  physical  and 
chemical  properties.  What  are  salts?  How  are  they 
classified?  What  are  chlorides  and  how  may  they  be 
prepared?  Give  their  chief  physical  and  chemical  proper¬ 
ties.  What  are  sulphides?  How  may  they  be  prepared? 
Give  their  chief  physical  and  chemical  properties.  What 
other  classes  of  salts  are  of  importance?  How  are  they 
usually  prepared?  Give  some  of  their  physical  and  chem¬ 
ical  properties.  Note  the  solublity  of  a  few  bases  and  salts 
on  page  544  in  Smith. 


CHAPTER  II 


A  PRELIMINARY  STUDY  OF  SOLUBILITY 

Experiment  1 

THE  SOLUBILITY  OF  CHLORIDES 

a.  In  separate,  clean  test  tubes,  place  about  2  cc.  of  each 
of  the  twenty-six  salt  solutions  listed  in  the  appendix8  and 
label  each  test  tube  with  the  formula  of  its  contents.  To 
each  of  these  in  turn,  add  hydrochloric  acid37.  If  the  first 

r. 

few  drops  of  acid  cause  a  precipitation38,  continue  to  add  the 
acid  as  long  as  it  gives  a  precipitate  in  the  clear  zone  which 
forms  above  after  the  precipitate  has  been  allowed  to  settle. 
Decant  the  liquid  from  each  of  the  precipitates  and  add  hy¬ 
drochloric  acid  to  them.  Do  any  dissolve?  Record  your 
results19-25  and  state  your  conclusions.  Which  chlorides 
are  soluble  in  water?  Insoluble  in  water?  Soluble  in  dilute 
acid  solutions  ?  Insoluble  ? 

b.  Repeat  a,  using  solutions  of  lead,  silver,  and  mer¬ 
curous  nitrates  and  any  soluble  chloride,  as  ammonium 
chloride7.  Do  these  results  agree  with  those  in  a? 

Experiment  2 

THE  SOLUBILITY  OF  SULPHIDES 
1.  The  Solubility  of  Sulphides  in  Dilute  Acid  Solutions 

In  separate,  clean  test  tubes,  labelled  as  before,  place 
about  2  cc.  of  each  of  the  solutions  of  the  salts  of  the  metals 
and  make  the  solution  in  each  test  tube  acid  with  a  few 


26 


THE  SOLUBILITY  OF  SULPHIDES 


27 


drops  of  hydrochloric  acid.  Test  with  litmus  paper.  If 
the  hydrochloric  acid  gives  a  precipitate,  use  nitric  acid  in 
its  stead.  Through  a  clean  glass  jet  tube,  slowly  pass  hy¬ 
drogen  sulphide  in  excess  into  each  salt  solution  in  turn. 
Note  accurately  the  effects39  of  the  gas  and  record  your  re¬ 
sults  as  in  Experiment  119~25.  Save  the  precipitates  for 
2,  below. 

2.  The  Solubility  in  Alkaline  Polysulphides  of  the  Sul¬ 
phides  Insoluble  in  Dilute  Acids 

In  each  of  the  cases  in  1  in  which  a  precipitate  formed  in 
acid  solution,  decant  the  supernatant  fluid,  wash  the  residue 
twice  by  decantation40,  and  to  the  solid  still  remaining  in  the 
test  tube  add  ten  to  twelve  drops  of  yellow  ammonium  sul¬ 
phide,  diluted  with  an  equal  quantity  of  distilled  water.  Heat 
the  test  tube  gently.  Which  sulphides  dissolve? 

3.  The  Solubility  of  Sulphides  in  Alkaline  Solutions 

Arrange  other  2  cc.  samples  of  the  salt  solutions,  which 
failed  to  form  precipitates  in  1.  To  each  add  ammonium 
hydroxide  until  the  reaction  is  barely  alkaline  and  then  add 
ammonium  sulphide  in  slight  excess.  What  precipitates 
now  form  ?  Write  an  equation  for  each41. 

Summary 

Tabulate  the  solubility  of  the  metallic  sulphides: — 

i.  In  dilute  acid  solutions, 

ii.  In  alkaline  polysulphides, 

iii.  In  dilute  alkaline  solutions, 

iv.  In  water. 


28 


CLASSIFICATION  OF  CHEMICAL  REACTIONS 


Enclose  in  a  black  line  rectangle  in  the  table  the  in¬ 
soluble  sulphides  whose  metals  form  insoluble  chlorides. 

CHEMICAL  REACTIONS 

Chemical  reactions  are  the  changes  which  take  place  be¬ 
tween  substances  when  they  act  chemically  upon  one  an¬ 
other.  N early  every  element  and  every  compound  enter  into 
chemical  reactions,  but  the  ability  to  do  so  varies  widely 
with  different  substances.  Some  compounds  are  stable 
only  under  very  special  conditions.  Hence,  these  sub¬ 
stances  offer  little  resistance  to  an  alteration  in  their  com¬ 
position.  On  the  other  hand,  other  compounds  are  very 
stable  except  under  special  conditions.  These  offer  more 
resistance  to  an  alteration  in  their  composition.  Gases  and 
liquids  react  with  each  other  more  readily  than  do  solids 
with  either  or  with  themselves. 

CLASSIFICATION  OF  CHEMICAL  REACTIONS 

Most  chemical  reactions  may  be  subdivided  into  four 
general  classes. 

1.  Reactions  of  Direct  Combination 

2Mg  +  02  =  2MgO  HC1  +  NH3  =  NH4C1 

CaO  +  H20  =  Ca(OH)2  2BaO  +  O,  =  2Ba02 

2.  Reactions  of  Direct  Decomposition 

2HgO  =  2Hg  +  02  2KC1Q3  =  2KC1  +  302 
NH4C1  =  NH3  +  HC1  CaC03  =  CaO  +  C02 


2Ba02  =  2BaO  +  O. 


H2C204  =  H20  +  CO  +  C02 


CHEMICAL  EQUATIONS 


29 


3.  Metathetical  Reactions 

AgN03  +  HC1  =  AgCl  +  HNOs 

ZnS04  +  (NH4)2S  =  ZnS  +  (NH4)2S04 

BaHP04  +  2HN03  =  Ba(N03)2  +  H3P04 

NaOH  +  HC1  =  NaCl  +  H20 

Fe(OH)3  +  3HC1  =  FeCl3  +  3H20 

FeS  +  2HC1  =  FeCl2  +  H2S 

K2C03  +  H2S04  =  K2S04  4-  C02  +  H20 

HgCl2  4-  Cu  =  CuCl2  +  Hg 

CdCl2  +  H2S  =  CdS  4-  2HC1 

FeCl3  +  3NaOH  =  Fe(OH)3  +  3NaCl 

Al(OH),  +  NaOH  =  NaA102  +  2H20 

ZnO  +  2HN03  =  Zn(N03)2  +  H20 

Ba(OH)2  +  H2S04  =  BaS04  +  2H20 

2NH4C1  +  Ca(OH)2  =  CaCl2  +  2NH3  +  2H20 

2KBr  +-C1*  =  2KC1  +  Br2. 

4.  Reactions  of  Oxidation  and  Reduction 

3Fe  +  4H20  =  Fe304  4H2  Cu.0  4"  H2  =  Cu  4"  H20 

3H2S  +  8HN03  =  3H2S04  4-  8NO  4-  4H20 
6FeS04  4-  2HN03  4-  3H2S04  =  3Fe2(S04)3  4-  4H20 

EQUATIONS  TO  REPRESENT  CHEMICAL  REACTIONS 

One  of  the  chief  uses  of  the  symbols  of  elements  and  the 
chemical  formulas  of  compounds  is  to  enable  us  to  express, 
in  a  condensed  and  precise  form,  a  considerable  amount  of 


30  CHEMICAL  EQUATIONS 

information  respecting  chemical  changes.  These  changes 
are  called  reactions  and  they  are  expressed  in  the  form  of 
equations,  i.  Chemical  equations  show  qualitatively  what 
substances  enter  into  the  reaction  and  what  substances  are 
produced  by  the  reaction,  ii.  They  indicate  the  propor¬ 
tions  in  which  the  reacting  substances  act  upon  one  another, 
iii.  They  show  how  much  of  each  product  is  formed  as  a 
result  of  the  reaction..  A  knowledge  of  the  solubility  of 
acids,  bases,  and  salts  is  absolutely  necessary  in  order  to  be 
able  to  give  accurately  and  readily  the  equations  that  repre¬ 
sent  the  reactions  which  result  when  substances  act  chemi¬ 
cally  upon  one  another. 

In  order  to  write  a  chemical  equation  three  things  are 
essential:  1.  We  must  know  what  substances  react  and 
their  correct  chemical  formulas.  2.  We  must  know  what 
substances  are  formed  and  the  correct  chemical  formulas 
for  them.  3.  We  must  balance  the  equation,  that  is,  we 
must  choose  such  proportions  of  the  substances  that  the 
number  of  atoms  of  each  element  represented  in  each  mem¬ 
ber  of  the  equation  is  the  same. 

An  equation  states  the  proportions  by  weight  of  the  sub¬ 
stances  which  enter  into  the  reaction.  For  example,  barium 
chloride  reacts  with  sulphuric  acid  to  form  barium  sulphate 
and  hydrochloric  acid.  This  reaction  may  be  represented 
by  the  following  equation : 

BaCl2  +  H2S04  =  BaSQ4  +  2HC1 

208.3  +  98.1  =  233.5  +  72.9 

This  equation  means  that  by  weight  208.3  parts  of  bar- 


ELECTROLYTIC  DISSOCIATION 


31 


ium  chloride  always  reacts  with  98.1  parts  of  sulphuric  acid 
producing  233.5  parts  of  barium  sulphate  and  72.9  parts 
of  hydrochloric  acid.  For  parts  by  weight  we  may  substi¬ 
tute  any  unit  of  weight,  but  the  same  unit  must  be  used 
throughout  the  calculations.  It  is  thus  evident  that  if  we 
know  the  weight  of  one  substance  taking  part  in  the  re¬ 
action,  all  the  other  weights  involved  can  be  calculated. 

THE  THEORY  OF  ELECTROLYTIC  DISSOCIATION 

Since  so  many  of  the  reactions  of  qualitative  analysis 
take  place  in  solution,  it  is  necessary  at  this  time  to  consider 
the  theory  of  dissociation  in  solution  somewhat  in  detail. 
The  most  common  and  universal  fluid  medium  or  solvent  is 
water.  The  theory  of  electrolytic  dissociation  states  that 
the  molecules  of  acids,  bases,  and  salts,  on  entering  into 
water  solution  break  up  more  or  less  completely  into  posi¬ 
tively  and  negatively  charged  atoms,  or  groups  of  atoms, 
called  ions.  These  ions  cannot  exist  except  in  solution  in  the 
presence  of  other  ions  carrying  equivalent  charges  of  electric¬ 
ity  of  the  opposite  kind.  They  react  chemically  independ- 
dently  of  each  other  and  of  the  molecules  from  which  they 
were  originally  derived.  The  nature  of  this  dissociation  in 
these  three  classes  of  electrolytes  is  shown  by  the  follow¬ 
ing  equations  representing  reversible  reactions : 


+ 


HC1 


H  +  Cl 


H2SO 


2H  +  S04 


+ 


+ 


NaCl 


*=>  Na  +  Cl 


+ 


+  + 


NaOH  <=±  Na  +  OH  Ba(OH)2  <=±  Ba  +  20H 


32 


COMMON  POSITIVE  IONS 


The  positively  charged  ions  are  called  cations  and  the 
negatively  charged  ions,  anions.  Ions,  which  are  charged 
with  quantities  of  electricity  equivalent  to  that  of  the  hy¬ 
drogen  ion  or  of  the  chlorine  ion,  are  called  monovalent  ions ; 
those  charged  with  twice  this  quantity  of  electricity,  diva¬ 
lent  ions ;  and  those  carrying  a  charge  three  times  as  great 
as  that  of  the  ion  of  hydrogen  or  of  chlorine,  trivalent  ions. 
The  valence  of  the  ions  and  the  number  of  unit  charges  of 
electricity,  which  each  ion  carries,  is  denoted  by  signs  placed 
above,  or  at  the  right  upper  corner  of,  their  chemical  sym¬ 
bols  or  formulas.  In  the  case  of  electropositive  ions,  or 
cations, the  plus  sign  (  +  ),oradot  ( * ) , is  used  and, in  the  case 
of  the  electro-negative  ions',  or  anions,  the  minus  sign  (  — )  or, 
an  acute  accent  ('),  is  used. 

The  following  table,  taken  with  some  modifications  from 
Newth’s  Inorganic  Chemistry,  gives  a  number  of  the  com¬ 
mon  positive  and  negative  ions. 


I.  CATIONS 


Monovalent 

Divalent 

Trivalent 

+ 

+  + 

+  +  + 

Ag, 

Silver 

Pb, 

Lead 

Bi, 

Bismuth 

Hg, 

Mercurous 

Hg, 

Mercuric 

As, 

Arsenic 

Cu, 

Cuprous 

Cu, 

Cupric 

Sb, 

Antimony 

Na, 

Sodium 

Cd, 

Cadmium 

Fe, 

Ferric 

K, 

Potassium 

Sn, 

Stannous 

Cr, 

Chromium 

nh4 

,  Ammonium 

Fe, 

Ferrous 

Al, 

Aluminum 

H, 

Hydrogen 

Co, 

Cobalt 

Tetra  valent 

Ni, 

Nickel 

Mn, 

Manganese 

+  +  +  + 

Zn, 

Zinc 

Sn, 

Stannic 

Ba, 

Barium 

Sr, 

Strontium 

Ca, 

Calcium 

Mg, 

Magnesium 

COMMON  NEGATIVE  IONS 


33 


II.  ANIONS 


Monovalent 

Divalent 

Tri  valent 

F,  Fluoride 

Cl,  Chloride 

Br,  Bromide 

I,  Iodide 

CIO  3,  Chlorate 

OH,  Hydroxyl 

NO  3,  Nitrate 

C2H302,Acetate 
And  the  anions  of 
all  other  monobasic 
acids 

S04,  Sulphate 

S,  Sulphide 

SO  3,  Sulphite 
S203,  Thiosulphate 
CO  3,  Carbonate 
C204,  Oxalate 

C  4  H  4  0  6  ,T  art  rate 
And  the  anions  of 
all  other  dibasic 
acids 

P04,  Phosphate 
As04,  Arsenic 
As03,  Arsenious 
And  the  anions  of 
all  other  tribasic 
acids 

Pure  water,  pure  hydrogen  chloride,  and  pure  sugar  do 
not  conduct  the  electric  current.  If  sugar  is  dissolved  in 
water,  the  solution  is  still  a  non-conductor  of  electricity. 
If  hydrogen  chloride  is  dissolved  in  water,  the  solution  is  a 
fairly  good  conductor  of  electricity.  This  has  been  found  to 
be  the  case  for  all  aqueous  solutions  of  acids, bases,  and  salts, 
and  for  them  only.  Hence,  they  are  called  electrolytes. 
When  an  electric  current  is  passed  through  a  solution  of  hy¬ 
drochloric  acid, there  is  not  a  simple  case  of  conduction  as  when 
a  copper  wire  is  used;  but  hydrogen  separates  at  the  neg¬ 
ative  electrode  (cathode)  and  chlorine,  at  the  positive  elec¬ 
trode  (anode).  Now  it  is  evident  that  something  happens 
either  to  the  water  or  to  the  hydrochloric  acid,  when  they 
are  mixed;  because,  after  the  mixing,  the  solution  con¬ 
ducts  electricity  while  beforehand  neither  the  water  nor  the 
hydrogen  chloride  is  a  conductor.  Since  only  the  hydro¬ 
chloric  acid  is  affected  by  the  passage  of  the  current,  it  is 
reasonable  to  suppose  that  the  water  is  not  altered  in  the 
process  of  solution. 


34 


ELECTROLYTIC  DISSOCIATION 


Ions  have  certain  peculiar  properties  but  when  their 
electrical  burdens  are  discharged,  the  atoms,  or  the  atomic 
groups,  of  the  former  ion  assume  the  properties  of  nascent 
atoms,  or  atomic  groups,  and  react  accordingly.  For 

example,  the  ions  of  potassium  sulphate,  2K  and  S04, 
when  they  exist  in  the  presence  of  each  other 
in  the  ionic  condition,  do  not  decompose  water; 
but  when  the  electric  charges  of  these  ions  are  discharged, 
as  by  the  passage  of  an  electric  current,  then  the  atoms  of 
the  element  potassium  react  with  the  water,  forming  potas¬ 
sium  hydroxide  and  free  hydrogen  and  the  sulphu¬ 
ric  acid  groups  decompose  water,  forming  sulphuric 
acid  and  liberating  oxygen.  Atoms  of  elements,  or  groups 
of  atoms,  which  do  not  act  upon  water,  when  they 
are  freed  at  the  electrodes  by  the  discharge  of  the  electricity 
of  the  ions,  combine  to  form  free  molecules,  since  after  giving 
up  their  electric  charges  they  no  longer  repel  each  other. 
For  example,  two  negative  bromine  atoms  combine  to  form 
one  bromine  molecule,  two  negative  hydroxyl  groups  com¬ 
bine  to  form  one  hydrogen  dioxide  molecule,  and  one  posi¬ 
tive  mercury  ion  is  changed  into  a  molecule  of  mercury. 

The  ions  alone  are  the  medium  by  which  the  electric  cur¬ 
rent  is  transmitted  through  solutions.  The  current  of  elec¬ 
tricity  which  passes  through  a  solution  is,  in  fact,  conveyed 
by  the  ions.  The  molecules  which  are  not  dissociated  into 
ions  do  not  take  part  in  the  conduction  of  the  electric  cur¬ 
rent.  The  more  ions  there  are  in  a  unit  volume,  the  better 
the  solution  conducts  electricity.  In  other  words,  the  more 


ELECTROLYTIC  DISSOCIATION 


35 


a  substance  is  ionized,  the  greater  the  conductivity  of  its 
solution.  The  extent  of  electrolytic  dissociation  varies 
greatly  with  different  electrolytes  but  in  all  cases  it  increases 
with  dilution.  Ionization  is  practically  complete  with  very 
great  dilution.  For  every  degree  of  dilution  there  exists  a 
certain  state  of  equilibrium  between  the  ions  and  the  undis¬ 
sociated  molecules. 

In  terms  of  the  theory  of  electrolytic  dissociation,  acids, 
bases,  and  salts  may  be  defined  as  follows: 

1.  Acids  are  hydrogen  compounds  which  upon  electro¬ 
lytic  dissociation  decompose  in  part  or  entirely  into  cations 

+ 

of  hydrogen,  H,  and  anions  of  non-metals,  or  anions  com¬ 
posed  of  negative  atomic  groups.  The  hydrogen  ion  is  the 
characteristic  cation  of  all  acids  and  whenever  it  is  present 
acid  properties  are  produced. 

2.  Bases  are  hydroxyl  compounds  which  upon  electro¬ 
lytic  dissociation  are  separated  partly  or  entirely  into  hy¬ 
droxyl  ions,  OH,  and  metallic  ions.  The  hydroxyl  ion 
is  the  characteristic  anion  of  all  bases  and  whenever  it  is 
present  basic  properties  are  produced. 

3.  Salts  are  compounds  of  metals  which  upon  electro¬ 
lytic  dissociation  are  separated  entirely  or  in  part  into  basic 
cations  and  acidic  anions. 

Chemical  reactions,  between  electrolytes  in  water  solu¬ 
tion,  are  really  reactions  between  the  ions.  That  is  to  say, 
the  reactions  which  take  place  in  aqueous  solution  are  de¬ 
pendent,  for  the  most  part,  upon  the  presence  of  ions. 
The  greater  the  concentration  of  the  ions  of  a  substance  in 


36 


ELECTROLYTIC  DISSOCIATION 


the  solution,  the  greater  is  its  chemical  activity,  since  it  is 
the  free  ions  only  which  enter  into  reactions. 

The  chemical  properties  of  aqueous  solutions  of  salts, 
acids,  and  bases,  depend  largely  upon  the  properties  of  the 
free  ions  which  they  contain.  For  example,  in  all  solutions 

H — h 

of  barium  salts,  the  presence  of  the  barium  ion,  Ba,  can  be 
proved  by  one  and  the  same  reagent ;  namely,  the  sulphate 

ion,  S04.  The  barium  ion  always,  without  regard  to  the 
large  number  of  combinations  which  it  may  form,  unites 
with  the  sulphate  ion  to  produce  slightly  dissociated  barium 
sulphate,  which  is  not  soluble. 

Again,  silver  nitrate  is  a  reagent  for  the  chlorine  ion,  Cl. 
All  the  metallic  chlorides  and  similar  compounds  give  with 
this  reagent  a  precipitate  of  silver  chloride.  Silver  nitrate 
does  not,  however,  react  with  all  chlorine  compounds.  The 
presence  of  chlorine  in  potassium  chlorate  is  not  indicated 
by  silver  nitrate.  Silver  nitrate  is  not  a  reagent  for  chlo¬ 
rine  compounds  in  general.  It  is  only  a  reagent  for  the  chlo¬ 
rine  ion.  When  potassium  chlorate  dissolves  in  water,- it  dis- 
+  — 

sociates  into  the  ions  K  and  C103  and  therefore  it  does  not 
contain  chlorine  as  a  separate  ion  but  only  as  a  constituent 

.oi  a  more  complex  ion,  C103.  When  silver  nitrate 
is  added  to  a  solution  of  potassium  chlorate,  silver  chlo¬ 
ride  is  not  formed, because  chlorine  ions  are  not  jmesent  and 
a  precipitate  does  not  appear  because  all  the  possible  com¬ 
pounds  are  soluble  in  water. 


REVIEW  QUESTIONS 


37 


It  follows  from  these  considerations  that  in  qualitative 
analysis  we  test  for  the  ions  which  may  be  present.  Since 
the  ions  serve  for  the  identification  of  the  respective  sub¬ 
stances,  a  knowledge  of  the  ionic  conditions  of  salts,  acids, 
and  bases  is  of  much  importance.  In  our  future  work  in 
this  course  we  shall  consider,  therefore,  the  nature  and  the 
relation  of  the  ions  of  the  various  substances  studied. 

Questions 

Reference  in  Smith:  Pages  273  and  274 
What  are  chemical  reactions?  What  substances  enter 
into  reactions?  What  substances  react  most  readily? 
Name  the  four  general  classes  of  chemical  reactions.  De¬ 
fine  each  and  give  several  examples.  How  are  chemical  re¬ 
actions  usually  represented?  What  three  things  do  chem¬ 
ical  equations  show?  What  three  things  must  we  know  in 
order  to  write  chemical  equations?  Discuss  the  equation 
representing  the  reaction  between  barium  chloride  and  sul¬ 
phuric  acid. 

Under  what  conditions  do  most  of  the  reactions  of  qual¬ 
itative  analysis  take  place?  What  is  the  most  common  sol¬ 
vent?  What  probably  occurs  when  acids,  bases,  or  salts 
dissolve  in  water?  What  are  ions?  How  do  they  react? 
Show  by  equations  the  nature  of  the  dissociation  of  acids, 
bases,  and  salts.  What  are  cations  ?  Anions  ?  How  is  the 
valence  of  an  ion  designated  ?  Name  a  few  of  the  most  com¬ 
mon  monovalent  cations.  Divalent  cations.  Trivalent  cat¬ 
ions.  Monovalent  anions.  Divalent  anions.  Trivalent. 


anions. 


38 


REVIEW  QUESTIONS 


What  is  the  effect  of  an  electric  current  upon  pure  water? 
Upon  pure  hydrogen  chloride?  Upon  pure  sugar?  Is  the  effect 
different  if  the  sugar  is  dissolved  in  water?  If  the  hydro¬ 
gen  chloride  is  dissolved  in  water?  What  happens  when  a 
current  of  electricity  passes  through  a  solution  of  hydro¬ 
chloric  acid?  Which  is  affected  by  the  electricity,  the  water 
or  the  hydrochloric  acid?  What  happens  when  the  electric 
charges  of  the  ions  are  removed?  Illustrate  this  fully. 
How  is  an  electric  current  conducted  through  solutions? 
What  is  the  relation  of  the  non-dissociated  molecules  to  the 
passage  of  an  electric  current  ?  What  can  you  say  of  the  ex¬ 
tent  of  ionization  ? 

Define  acids,  bases,  and  salts  in  terms  of  the  ionic  theory. 
What  is  the  nature  of  chemical  reaction  in  water  solution  ? 
Upon  what  does  the  chemical  reactivity  of  &  solution  de¬ 
pend?  The  chemical  properties  of  such  solutions?  Give 
two  illustrations.  For  what  do  we  test  in  qualitative  analy¬ 
sis? 

Which  chlorides  are  insoluble  in  water?  In  acids? 
Soluble  in  water?  In  acids?  What  is  the  action  of  any 
soluble  chloride  on  any  soluble  salt  of  lead,  silver,  or  mer¬ 
curous  mercury?  Why  are  precipitates  not  formed  in  the 
solutions  containing  chlorides?  In  all  the  solutions? 
What  is  the  solubility  of  mercurous  chloride  in  water?  In 
acids?  Of  silver  chloride  in  water?  In  acids?  Of  cadmi¬ 
um  chloride  in  water?  In  acids? 

Bearing  in  mind  the  solubility  of  chlorides  complete  the 
following  equations: 


SOLUBILITY  OF  HYDROXIDES 


39 


ZnS04  +  NaCl  =  ?  SbCl3  +  A1C13  =  ? 

HgN03  +  KC1  =  ?  Ca(N03)2  +  HC1  =  ? 

Pb(N03)2.  +  CaCl2  -  ? 

Which  of  the  eleven  sulphides,  that  are  insoluble  in  di¬ 
lute  acid  solutions,  are  soluble  in  alkaline  poly  sulphides? 
What  are  the  products-  formed  when  these  sulphides  dis¬ 
solve  in  yellow  ammonium  sulphide?  Represent  the  reac¬ 
tions  by  equations.  Make  a  list  of  the  formulas  of  the  metallic 
sulphides  soluble  in  water.  Of  those  insoluble  in  dilute 
acids.  Of  those  soluble  in  dilute  acids  but  insoluble  in  water. 

Bearing  in  mind  the  solubility  of  sulphides  in  water,  in 
dilute  acids,  and  in  alkaline  polysulphides,  complete  the 
following  equations25 : 

BaCl2  +  H2S  =  ?  As2S3  +  (NH4)2S2  =  ? 

Zn(N03)2  +  (NH4)2S  =  ?  CuCl2  +  H2S  =  ? 

Sr(N03)2  +  (NH4)2S  =  ?  CdS04  +  K2S  =  ? 

MnS04  +  H2S  =  ?  SbCl3  +  (NH4)2S2  =  ? 

Show  that  substances  can  be  separated  from  a  mixture  by 
making  use  of  the  difference  in  solubility  of  the  substances. 

Experiment  3 

THE  SOLUBILITY  OF  HYDROXIDES 

1.  The  Reaction  of  Fixed  Alkali  Hydroxide  with  the 
Metallic  Salt  Solutions 

Arrange  and  label  as  before  about  2  cc.  of  each  of  the 
twenty-six  salt  solutions.  To  each  of  these  in  turn,  add  a 
few  drops  of  the  ten  per  cent  solution  of  sodium  hydroxide. 
For  calcium,  strontium,  and  barium  salts  use  the  “carbon¬ 
ate  free”  sodium  hydroxide.  If  the  r 

'ffRST  fzw  of  SO~ 


40 


SOLUBILITY  OF  CARBONATES 


ditim  hydroxide  cause  a  precipitation,  continue  to  add  the 
sodium  hydroxide  as  long  as  it  produces  a  precipitate  in  the 
clear  zone  which  forms  above  after  the  precipitate  is  allowed 
to  settle.  Then  add  a  decided  excess  of  sodium  hydrox¬ 
ide.  Does  the  precipitate  redissolve  ?  Keep  notes  as  be¬ 
fore  and  write  equations  in  those  cases  in  wdiich  you  are  sure 
that  a  reaction  takes  place42, 43. 

2.  The  Reaction  of  Volatile  Alkali  Hydroxide  with  the 
Metallic  Salt  Solutions 

Repeat  1,  using  ammonium  hydroxide  from  your  desk  in 
place  of  the  ten  per  cent  solution  of  sodium  hydroxide 
Keep  notes  as  before  and  write  the  equations43’ 44  as  in  1. 

3.  The  Effect  of  Ammonium  Chloride  in  Preventing  Precipi¬ 
tation  by  Ammonium  Hydroxide 

Arrange  other  2  cc.  samples  of  those  salt  solutions  which 
have  given  permanent  precipitates  with  ammonium  hydrox¬ 
ide  in  2.  To  each  of  these  in  turn,  add  an  equal  volume  of 
ammonium  chloride  and  then  ammonium  hydroxide  as  in 
2.  Howt  do  these  results  differ  from  those  in  2  ? 

Summary 

Tabulate  all  of  the  data  obtained  in  1,  2,  and  3. 

Experiment  4 

THE  SOLUBILITY  OF  CARBONATES 

To  about  2  cc.  of  each  of  the  solutions  of  the  metallic 
salts  in  turn,  add  enough  sodium  carbonate  solution  to  turn 
litmus  paper  blue.  Write  notes  and  equations  as  before 
but  remember  that,  with  sodium  carbonate,  silver,  mer- 


NON-REVERSIBLE  REACTIONS 


41 


curous  mercury,  cadmium,  ferrous  iron, manganese,  calcium, 
strontium,  and  barium  form  normal  carbonates  as  BaC03; 
lead,  copper,  cobalt,  nickel,  zinc,  and  magnesium  form  basic 
carbonates,  as  Zn2(0H)2C03;  ferric  iron,  chromium,  and 
aluminum  form  hydroxides ;  mercuric  mercury  forms  a  mix¬ 
ture  of  carbonate  and  oxide,  HgC03,  3HgO;  antimony, 
an  oxide;  stannous  tin,  stannous  acid,  H2Sn02;  stannic 
tin,  stannic  acid,  H2Sn03;  and  bismuth,  a  basic  carbonate, 
Bi2Q2CQ3. 

Cd(N03)2  +  Na2C03  =  CdC03  +  ? 

4Hg(NOs)2  +  4Na2C03  =  HgCQ3,  3HgO  4-  ?  4-  3C02 

SnCl2  +  Na2C03  4-  H20  =  H2SnQ2  +  ? 

2Co(N03)2  4-  2Na2C03  +  H20  =  Co2(OH)2C03  4-  ? 

2Bi(N03)3  4-  3Na2C03  4  Bi202C03  4-  ? 

REVERSIBLE  AND  NON-REVERSIBLE  REACTIONS 

From  another  viewpoint,  chemical  reactions  may  be 
divided  into  two  general  classes;  namely,  reversible  re¬ 
actions  and  non-reversible  reactions. 

NON-REVERSIBLE  REACTIONS 

In  these  cases,  the  reaction  can  not  be  made  to  proceed 
in  the  opposite  direction,  that  is,  they  can  not  be  reversed. 

2AgaO  =  4Ag  +  02  2KC1Q3  =  2KC1  +  302 

2Mg  +  O,  4  2MgO  Fe.+  S  -  FeS 

These  reactions  all  run  to  completion  from  left  to  right, 
provided  sufficient  time  is  allowed,  but  in  none  of  the  cases 


42 


REVERSIBLE  REACTIONS 


can  the  products  formed  be  converted  directly  into  the 
original  starting  substances. 

REVERSIBLE  REACTIONS 

In  these  cases,  on  the  other  hand,  the  reaction  is  capable 
of  taking  place  in  either  direction  and  it  may,  or  may  not, 
run  to  completion,  depending  upon  the  conditions  of  the  ex¬ 
periment.  If  steam  is  passed  over  red-hot  iron,  the  reac¬ 
tion  is  as  follows  : 

3Fe+4H20  =  Fe304+4H2 

If  the  hydrogen  that  is  formed  is  allowed  to  escape,  the 
iron  is  completely  converted  into  the  oxide;  otherwise,  it 
is  not.  If  hydrogen  is  passed  over  finely  divided,  incandes¬ 
cent  magnetic  oxide  of  iron,  Fe304,  the  reaction  is  as  fol¬ 
lows: 

Fe304  +  4H2=  3Fe+  4H20. 

Here  again,  if  the  steam  is  allowed  to  escape,  the  reac¬ 
tion  runs  to  completion  and  none  of  the  oxide  is  left.  When 
it  is  desired  to  call  attention  to  the  fact  that  a  reaction  is  re¬ 
versible,  it  is  generally  indicated  by  double  arrows  as  fol¬ 
lows: 

Fe304  +  4H2  ^  3Fe  +  4H20 

Another  typical  reversible  reaction  is  that  of  zinc  sul¬ 
phate  and  hydrogen  sulphide  in  neutral  solution.  If  hydro¬ 
gen  sulphide  is  passed  into  a  neutral  solution  of  zinc  sul¬ 
phate,  a  white  precipitate  of  zinc  sulphate  and  at  the  same 
time  free  sulphuric  acid  are  formed. 

ZnS04  +  H2S  <=±  ZnS  +  H2S04 


